During which of Piaget's stages do infants develop an understanding that objects continue to exist even when they are not seen?

Infants develop an understanding that objects continue to exist even when they are not visible during the sensorimotor stage of Piaget's theory of cognitive development. This concept is known as object permanence. In this stage, which occurs roughly from birth to around 2 years of age, children begin to understand that objects have an existence independent of their perception. Before developing this understanding, infants may react as if an object has disappeared when it is hidden from view.

As they progress through this stage, they will start to search for hidden objects, indicating their realization that these objects are still present even if they cannot see them. This cognitive breakthrough is crucial for further cognitive development and lays the foundation for more complex understanding of the world around them. The other stages, such as the preoperational stage, concrete operational stage, and formal operational stage, focus on other aspects of cognitive development and come after the sensorimotor stage.